The invention relates generally to cementing operations for wellbores. More specifically, the invention relates to a method and apparatus for cementing casing in a wellbore.
In the petroleum industry, wells are drilled in selected formations in an effort to produce hydrocarbons in commercially feasible quantities. During drilling operations for a typical oil or gas well, various earth formations are penetrated. To complete the well, casing is installed into the drilled wellbore.
Referring to FIG. 1, an example casing assembly 20 used in some oil and gas wells is shown. The casing assembly 20 for a given well is typically selected with an outer diameter that is small enough to go into the hole and still leave room for a cement layer 22 around the casing assembly 20, and an inner diameter that is large enough for the passage of downhole tools. Typically, as joints of the casing assembly 20 are connected to form a conventional casing string, the casing string is gradually moved downhole into the well. Once the desired length of a casing assembly 20 is connected, the casing assembly 20 is suspended or xe2x80x9chungxe2x80x9d in the well, either from the surface or from the end of a previously cemented casing.
A casing assembly 20 may include a guide shoe (not shown) at the bottom of the casing assembly 20 to guide the casing assembly 20 as it is lowered into the well. A guide shoe prevents the casing assembly 20 from snagging on the wall of the wellbore 14 as it is lowered into the well. A fluid passage is typically formed through the center of the guide shoe to allow drilling fluid to flow up into the guide shoe as the casing assembly 20 is lowered into the wellbore 14. The fluid passage also allows cement pumped down the casing assembly 20 to flow downhole and out of the casing assembly 20 during cementing operations.
Cementing of the casing assembly 20 in the well is typically done by pumping a volume of cement into the casing assembly 20 sufficient to fill the annulus between the casing assembly 20 and the wellbore 14, followed by pumping displacement fluid on top of the cement to displace the cement down the casing assembly 20 and up the annulus between the casing assembly 20 and wellbore 14. The volume of cement required to fill the annulus between the casing assembly 20 and the wellbore 14 can be calculated from the geometry of the wellbore 14 and the geometry of the casing assembly 20 inserted in the wellbore 14.
Cementing techniques are well developed for single-bore wells. However, multilateral wells are becoming increasingly more desirable to improve production. A bore leading from the surface is referred to as a primary or main wellbore. Each of directional wellbores extending from the primary wellbore is referred to as a lateral wellbore. The junction between a primary wellbore and one or more lateral wellbores is referred to as a wellbore junction.
Casing and cementing in a multilateral well presents a greater challenge than for uni-bore wells, especially in providing support and pressure integrity at the wellbore junction between the primary wellbore and a lateral wellbore. Existing cementing technology for multilateral wells makes use of hardware components, such as cement retainers, packers, and diverters, which are permanently set in the casing assembly during cementing operations that must be milled to clear the path for subsequent drilling operations. At a wellbore junction, the milling of the hardware components and cement in the internal volume of the wellbore may cause damage at the wellbore junction. This milling operation can also be time consuming and costly because of the number of downhole trips required.
In general, an improved cementing tool for cementing a casing assembly at a junction of plural wellbores is provided. For example, the cementing tool includes a body, an anchoring mechanism adapted to anchor the body within the casing assembly, and a flow conduit adapted to channel cement flow to an annular region outside the casing assembly. The anchoring mechanism is adapted to be released to enable retrieval of the cementing tool from the casing assembly.
Other or alternative features will be apparent from the following description, the drawings, and the claims.